1. Field of The Invention
The invention relates to a variable attenuator for use in optical fiber communication and optical network technology, and particularly to a motor driven variable attenuator with a linear motion mechanism.
2. The Related Art
A fiber optic attenuator is a passive optical component for reducing optical power propagating in a fiber, and may perform fixed or variable attenuation. Optic attenuators are widely used in optical transmission systems and optical networks, and especially in optical wavelength division multiplexer (WDM) networks which are closely related to the "Project of Information Highway". A motor driven optical variable attenuator (MDOVA) is a new device used in WDM networks and is able to automatically maintain the receiving power at a certain level so that the performance of the network can be greatly improved.
Although the MDOVA is a very practical device, only one patent discloses the corresponding content. U.S. Pat. No. 5,745,634 uses a gearbox to realize linear motion and a spring is used to reduce backlash. This complicated structure can only be housed in a large device. Furthermore, the resulting linear motion is inadequate. Setting this OVA device at a certain attentuation value will not result in very good resolution. To overcome this disadvantage, an optical detector is used in the OVA module to test the real optical power. Such a device is rather complicated and dramatically increases the cost of the OVA.
In addition, the prior art does not address the oscillation phenomenon in the attenuation spectrum, wherein such oscillation is caused by interference between two optical faces of a neutral density filter. This causes problems when the OVA is used in a WDM system or network thereby limiting its application.
Therefore, an object of the invention is to provide a cost effective and functionally reliable motor driven variable attenuator having a simple structure.